1. Field of the Invention
The present invention relates to a medical manipulator and, more particularly, to a medical manipulator having a simple mechanism and excellent in operability and safety.
2. Description of the Related Art
Referring to FIG. 13, laparoscopic cholecystectomy forms three small incisions 151, 152 and 153 in the abdominal wall, fits tracheal tubes 154 in the incisions 151, 152 and 153, inserts an endoscope 161, and forceps 171 and 172 through the tracheal tubes 154 into the abdomen. An operator 160, usually, a surgeon, conducts an operation, watching an image taken by the endoscope 161 and displayed on the screen of a monitor 162. Laparoscopic cholecystectomy reduces physical load on the subject and reduces the number of days for which the convalescent patient is obliged to stay in the hospital before leaving the hospital because laparoscopic cholecystectomy does not need to incise the abdominal wall. The field to which such a surgical operation is applicable is expected to expand.
Studies have been made for the development of techniques relating to remote-controlled robots, such as master-slave manipulators, to be applied to the medical field, and some techniques have been applied to clinical purposes (http://www.computermotion.com, http://www.intuitivesurgical.com). Techniques relating to remote-controlled robots provide a master-slave manipulator system including a master arm to be operated by an operator, and a slave arm for actually treating a diseased part, completely separated from the master arm. Electric signals corresponding to instructions given by operating the master arm are transmitted to the slave arm. Usually, the master arm and the slave arm are articulated arms having at least six degrees of freedom of motion. The master-slave manipulator system is a complicated system including a controller for controlling the joints of the articulated arms, an electrical control system, and many parts including wiring lines.
The inventors of the present invention proposed previously a simple medical manipulator (robotic forceps) developed by applying robot techniques to a conventional pair of forceps as shown in FIG. 14 in JP2000-350735A. Referring to FIG. 14, this previously proposed medical manipulator comprises a control unit 20 including a position controller 23 and an operation controller 24, a connecting unit 30 having one end connected to control unit 20, a working unit 10 connected to the other end of the connecting unit 30 and including support devices 15 and 16 supporting an end effector having operating members 14 for motions with at least two degrees of freedom, and a controller, not shown, for changing the positions of the operating members 14 of the end effector by controlling the support devices 15 and 16 according to instructions given by the position controller 23 and operating the operating members 14 of the end effector according to instructions given by the operation controller 24.
The inventors of the present invention proposed previously a medical manipulator as shown in FIG. 15 having degrees of freedom of motion suitable for suture and ligation in JP2002-102248A. This medical manipulator comprises a working unit 10, a control unit 20, and a connecting unit 30 having opposite ends respectively connected to the working unit 10 and the control unit 20. The working unit 10 includes a support device capable of turning about a first axis 11 perpendicular to the axis 31 of the connecting unit 30, and a second axis perpendicular to the first axis 11, and an end effector for treating a diseased part. The end effector has a gripper 14 is capable of turning about an axis substantially parallel to the second axis 12. The working unit 10 has a pitching joint 15 and a rolling joint 16 for moving the gripper 14 with two degrees of freedom. The control unit 20 includes a position controller 23 capable of turning about a third axis 21 perpendicular to the axis 31 of the connecting unit 30 and a fourth axis 22 perpendicular to the third axis 21, and an operation controller 24 to be operated by an operator. The operator grips the operation controller 24. The wrist of the operator gripping the operation controller 24 turns about an axis substantially parallel to the fourth axis 22. The gripping motion of the gripper 14 for treating a diseased part is controlled by operating the operation controller 24.
This previously proposed medical manipulator, differing from the remote-controlled master-slave manipulator, is formed by connecting the control unit (master unit) and the working unit, i.e., hand or forceps (slave unit) by the connecting unit, and is capable of achieving both simple, reliable, quick, large operations that can be performed by the operator, which is an advantage of the conventional forceps, and delicate, difficult operations and operations from difficult directions, which is an advantage of the manipulator. Since the working unit is provided with joints for bending and turning motions, the position of the end effector can freely be adjusted. Therefore, suturing and ligating operations from various directions, which have been difficult for the conventional forceps to perform, can easily be performed. The operator is able to use the medical manipulator and the conventional forceps simultaneously by operating the medical manipulator by the right hand and operating the forceps by the left hand. The simple, compact medical manipulator is inexpensive.
Medical instruments, particularly, surgical instruments, as well as medical robots, cannot be used for surgical operations unless those instruments are sterilized and cleaned. Generally, the working parts of medical robots, medical devices and surgical instruments are smeared with the blood and tissues of subjects of operations, and hence need to be washed clean and to be sterilized. At least the working unit, that comes into contact with the subject, of a large device can be removed from the main unit or can be separated from the control unit for cleaning and sterilization. Therefore, it is essential that the working units of medical robots, medical devices and surgical instruments are separable from the control units. The working unit separated for sterilization from the control unit must be capable of being combined with the control unit at a predetermined position relative to the control unit and in a predetermined orientation relative to the control unit.
Generally, a robot must be capable of a resetting operation, i.e., an initializing operation, when the robot is connected to a power source. The initializing operation operates the joints of the robot according to a predetermined sequential procedure to detect the arrival of the joints at their initial positions by initialization sensors incorporated into the joints, sets the joints in initial angular positions, and resets incremental encoders respectively combined with the output shafts of motors. It is very troublesome to operate a medical robot for initialization for returning the medical robot to its initial positional state during a surgical operation. Thus, it is desired that such an initializing operation is avoided as far as possible in a tense situation of a surgical operation. Therefore, it has been desired to develop a medical robot that can immediately be used after the same has been connected to a power source without requiring any initializing operation.
The medical manipulator previously proposed by the inventors of the present invention is provided integrally with the master unit and the slave unit, the operator who operates the medical manipulator must bear the weight of the medical manipulator. Therefore, it is the most important problem to form the medical manipulator in a small, lightweight structure. Therefore, it is very difficult, in respect of available spaces and allowable weight, to combine initialization sensors with the joints and other necessary parts. Even if initialization sensors could be combined with the joints and other necessary parts, a large number of wiring lines are necessary for connecting the initialization sensors to the associated parts and devices, which increases the weight of the medical manipulator and deteriorates the operability of the medical manipulator significantly.
Although a robot capable of always securing an absolute position without performing an initializing operation can be formed by providing the robot with absolute encoders, the absolute encoders are larger and need more wiring lines than incremental encoders. Thus, the employment of absolute encoders is not suitable for the medical manipulator previously proposed by the inventors of the present invention.